The present application relates to liquid crystal display panels and electronic apparatus including a viewing angle control sub-pixel, and particularly to a liquid crystal display panel and electronic apparatus in which a viewing angle control sub-pixel operates based on the transverse electric field system.
The liquid crystal display panel has features of lighter weight, smaller thickness, and lower power consumption compared with the cathode ray tube (CRT) and therefore is used as a display unit in many pieces of electronic apparatus. The liquid crystal display panel is to display an image by changing the orientation of liquid crystal molecules aligned along a predetermined direction by an electric field to thereby change the amount of light transmitted through the liquid crystal layer. Among such liquid crystal display panels are a reflective display panel, in which ambient light is incident on the liquid crystal layer and is reflected by a reflective plate to be transmitted through the liquid crystal layer again and be output, a transmissive display panel, in which incident light from a backlight device is transmitted through the liquid crystal layer, and a semi-transmissive display panel having the characteristics of both the reflective display panel and the transmissive display panel.
As the method for applying the electric field to the liquid crystal layer of the liquid crystal display panel, a method of the vertical electric field system and a method of the transverse electric field system are known. In the liquid crystal display panel of the vertical electric field system, an electric field along substantially the vertical direction is applied to liquid crystal molecules by a pair of electrodes sandwiching the liquid crystal layer. As the liquid crystal display panel of this vertical electric field system, display panels of the twisted nematic (TN) mode, the vertical alignment (VA) mode, the multi-domain vertical alignment (MVA) mode, the electrically controlled birefringence (ECB) mode, etc. are known. In the liquid crystal display panel of the transverse electric field system, a pair of electrodes insulated from each other are provided on the internal surface side of one of a pair of substrates sandwiching the liquid crystal layer, and an electric field along substantially the lateral direction is applied to liquid crystal molecules. As the liquid crystal display panel of this transverse electric field system, a display panel of the in-plane switching (IPS) mode, in which the pair of electrodes do not overlap with each other in plan view, and a display panel of the fringe field switching (FFS) mode, in which the pair of electrodes overlap with each other in plan view, are known.
In the IPS-mode liquid crystal display panel, the pair of electrodes as a pixel electrode and a common electrode are formed into a comb-teeth shape so that they may be interdigitated with each other, in such a state as to be electrically insulated from each other, and an electric field along the lateral direction is applied to the liquid crystal between the pixel electrode and the common electrode. Among the IPS-mode liquid crystal display panels are display panels in which both electrodes are formed in the same layer and display panels in which the electrodes are formed in layers different from each other with the intermediary of an insulating film. This IPS-mode liquid crystal display device has an advantage that the viewing angle is wider than that of the liquid crystal display device of the vertical electric field system.
In the FFS-mode liquid crystal display panel, the pair of electrodes as an upper electrode and a lower electrode are disposed in layers different from each other with the intermediary of an insulating film. Furthermore, slit apertures are provided in the upper electrode and an electric field along substantially the lateral direction passing through the slit aperture is applied to the liquid crystal layer. This FFS-mode liquid crystal display panel is increasingly used in recent years because it has an advantage that a wide viewing angle can be obtained and the image contrast can be improved.
As described above, the liquid crystal display panel of the transverse electric field system has a wide viewing angle. However, when confidential information that is not desired to be seen is displayed, it is preferable to employ a small viewing angle to prevent others from having visual contact with the displayed information. So, as shown in Japanese Patent Laid-open No. Hei 5-108023 (hereinafter, Patent Document 1), there has been known a method of adding a liquid crystal panel for viewing angle control to a liquid crystal panel for displaying and controlling the viewing angle characteristics. However, this method has a problem that the addition of the panel for viewing angle control greatly increases the thickness of the liquid crystal display panel. As a solution to this problem, as shown in Japanese Patent Laid-open No. 2007-156403 (hereinafter, Patent Document 2) and Japanese Patent Laid-open No. 2009-222747 (hereinafter, Patent Document 3), there has been known a method of adding a viewing angle control sub-pixel in addition to display sub-pixels of red (R), green (G), and blue (B) and controlling the viewing angle characteristics by controlling the voltage applied to the viewing angle control sub-pixel.
In the liquid crystal display panel including the viewing angle control sub-pixel disclosed in Patent Document 2, the display sub-pixel operates in the IPS mode of the transverse electric field system, and the viewing angle control sub-pixel operates in the ECB mode of the vertical electric field system. When light from the backlight is transmitted in the viewing angle control sub-pixel, the contrast is lowered due to light leakage and thus viewing the displayed image is difficult in the oblique viewing direction. Consequently, the viewing angle control effect can be exerted.
In the liquid crystal display panel including the viewing angle control sub-pixel disclosed in Patent Document 3, both the display sub-pixel and the viewing angle control sub-pixel operate in the FFS mode of the transverse electric field system. The slit aperture of the viewing angle control sub-pixel is extended at a right angle to the rubbing direction. Thus, when an electric field is applied between the pair of electrodes, liquid crystal molecules do not rotate in the direction parallel to the array substrate but are inclined to the perpendicular direction. Therefore, although no influence is given to the image on the display sub-pixels in the direct viewing direction, the contrast is lowered due to light leakage and thus viewing this image is difficult in the oblique viewing direction along which the liquid crystal molecules are inclined. Consequently, the viewing angle control effect can be exerted. The liquid crystal display panel disclosed in Patent Document 3, in which the viewing angle control sub-pixel is based on the transverse electric field system, has an advantage that manufacturing and driving thereof are easy because the viewing angle control sub-pixel and the display sub-pixel can be operated in the same mode and similar driving control can be carried out for both pixels.